This episode of the "Empire" podcast interviews Brian Catlos, author of "The Brilliant Kingdoms of Faith," about Isabella I of Castile. The discussion begins with background on Castile and its complex history of coexisting Christian, Muslim, and Jewish populations before Isabella's reign. The hosts and Catlos then delve into Isabella's life, her rise to power amidst political intrigue and the questionable legitimacy of her predecessor's heir, and her marriage to Ferdinand II of Aragon. A key takeaway is the nuanced perspective on Isabella, presented as both a powerful unifier of Spain and a ruthless figure responsible for the Inquisition and expulsion of religious minorities. The episode concludes by setting the stage for a future discussion on the Inquisition.